Page 147 - 89Zr-Immuno-PET:Towards a Clinical Tool to Guide Antibody-based Therapy in Cancer

89Zr (T1⁄2 =78.4 hrs) (BV Cyclotron VU, Amsterdam, the Netherlands) was coupled to rituximab via the bifunctional chelator N-succinyl-desferal. Methods used for radiolabeling have been described previously (8-10). The radiochemical purity was assessed by instant thin layer chromatography (iTLC) and high- performance liquid chromatography (HPLC). The immunoreactive fraction was assessed by Lindmo binding assay using either Ramos (patient 1, 2, 3) or Su-DHL4 (patient 4, 5, 6) cells. The endotoxin content was determined according to pharmacopeia using an endosafe PTS reader. Sterility of each 89Zr-rituximab batch was assured by performing a media fill immediately after final filter sterilization of each batch. The radiochemical purity, immunoreactivity and endotoxin content of every batch were assessed prior to administration to a patient. Manufacturing and radiolabeling were performed according to Good Manufacturing Practice (GMP) standards.
Patients received a therapeutic dose of rituximab (range 700-1000 mg) on
day 1 of cycle 1 of second line treatment, within 2 hours followed by 89Zr-rituximab
(10 mg, 74 MB +/- 10%) as an intravenous bolus injection. Venous blood samples
were scheduled at t=120 min (D0), 72 hrs (D3) and 144 hrs (D6) post injection
(p.i.). Whole blood and plasma radioactivity concentrations were measured with a
gamma well counter (Wallac 1480 Wizard, Turku, Finland). Radioactivity measurements obtained with venous blood samples were correlated with image- 7 derived blood pool measurements. Percentage injected dose (%ID) in blood pool
on D6 was calculated using image derived radioactivity concentrations and total
blood volume (11). Tracer availability is commonly defined as the concentration
of the tracer in the plasma fraction, therefore the total activity in plasma needs to
be calculated and compared to the total activity in whole blood.
Total activity in plasma on D6 was calculated from the venous blood samples, using standard hematocrit values (0.45 for males and 0,4 for females) and total blood volume. Total activity in whole blood was calculated from the venous blood samples and total blood volume. A two-tailed paired t-test was used to test for a difference between both measures of total activity.
Immuno-PET scans (Gemini TF-64/Ingenuity TF-128; Philips Healthcare, Best, the Netherlands), were acquired at D0, D3 and D6 p.i., and reconstructed as described previously (12). Each whole body immuno-PET scan was preceded by a 35 mAs low-dose computed tomography (ldCT) scan for attenuation and scatter correction. Immuno-PET scans were evaluated by a nuclear medicine physician, blinded for the 18F-FDG-PET and biopsy results. Lesions were considered positive
89Zr-rituximab-PET in lymphoma
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